The present invention relates to a driving tool for driving a fastener into a workpiece such as a wood building material.
A driving tool generally includes a driver blade extending from a piston reciprocally movable in a cylinder. A pneumatic pressure is applied to the piston, so that the driver blade is moved toward a workpiece such as a timber for driving a fastener such as a staple and a nail thereinto.
Laid open Japanese Patent Application Publication No. H09-109056 discloses a fixing structure of a driver blade to a piston. As shown in FIGS. 7 and 8, a piston 207 includes a piston body 207A and a boss 207B extending from one side of the piston body 207A toward a fastener driving direction. The boss 207B is formed with a fitting groove 207a extending in an axial direction of the boss 207B for fitting an upper region of a plate like driver blade 208. The boss 207B is also formed with a shaft hole 207b extending in a diametrical direction thereof. Further, the driver blade 208 is formed with a shaft hole 208a in alignment with the shaft hole 207b when the driver blade 208 is completely fitted into the fitting groove 207a. A shaft 209 extends through the shaft holes 207b and 208a thereby fixing the driver blade 208 to the piston 207. Incidentally, in FIGS. 5 and 6, a reference numeral 11 designates a piston ring assembled in a piston ring groove 107a. 
With such a conventional arrangement, the piston 207 and the driver blade 208 are subjected to machining for forming the shaft holes 207b and 208a and the shaft 209 is required for the mechanical connection, thereby increasing production cost and mechanical components. Further, local stress is imparted on the shaft 209, and shaft holes 207b, 208a due to load incurred by the fastener driving operation. Therefore, the shaft 209 may be broken and the shaft holes may be deformed. Furthermore, accurate alignment must be provided between the shaft holes 207b and 208a in order to allow insertion of the shaft 209 therethrough. To this effect, additional jig must be required in order to hold the piston 207 and the driver blade 208 at the alignment position. This lowers assembleability of the piston 207 and the driver blade 208.